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New Protein Booster May Lead to Better DNA Vaccines and Gene Therapy

New Protein Booster May Lead to Better DNA Vaccines and Gene Therapy

Scientists have discovered a new way to manipulate how cells function, a finding that might help advance an experimental approach to improving public health: DNA vaccines, which could be more efficient, less expensive and easier to store than traditional vaccines.

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Their approach, based on research results published this week in the journal Proceedings of the National Academy of Sciences, improves upon an existing laboratory technique, transfection, widely used to study how cells and viruses work.

Jaquelin Dudley, a professor of molecular biosciences at The University of Texas at Austin, and her team have developed a method for boosting the amounts of certain proteins a host cell produces when genes are delivered by transfection. Coaxing cells to produce novel proteins, such as those associated with viruses, is a key feature of DNA vaccines. Dudley's method causes cells to produce novel proteins at levels 5 to 20 times as high as with previous methods.

The researchers suggest that their finding might lead to better DNA vaccines, a relatively new method of vaccination that health experts say would increase vaccination rates, especially in the developing world. Whereas traditional vaccines train the body to attack viruses by introducing weakened forms of the virus, a DNA vaccine works differently, using a bit of DNA specified by a virus to prompt the production of proteins that lead to immunity.

By boosting the amount of proteins produced by the hosts' cells, Dudley's new method might invoke a stronger immune response in patients receiving a DNA vaccine. And, by making smaller vaccine doses possible, it might also reduce the risk that the patient's immune system would inadvertently attack healthy host cells.

The scientists’ discovery could also help advance another experimental approach: gene therapies, which treat genetic disorders by replacing or disrupting genes that aren't working properly. Gene therapies targeting Parkinson's, hemophilia, leukemia, cystic fibrosis and many other diseases are being developed, but gene therapies have proved difficult, as they sometimes induce a cancer or trigger an immune response against cells with the introduced genes. The new method for boosting novel protein production might prevent these effects by allowing the insertion of smaller amounts of DNA.

The method for boosting production of novel proteins in a host cell was discovered by accident. Dudley and her team were attempting to understand how mouse mammary tumor virus (MMTV), a virus related to HIV that causes breast cancer and leukemia, manipulates an infected host cell to keep the host's immune system from attacking it.

A bit of genetic material that was expected to produce lower levels of a certain protein instead caused cells to produce a lot more of it.

"Everything in the literature would indicate that something abnormal had happened," said Dudley. "But we went back and used several different detection methods to show that what we observed was real."

According to conventional wisdom, when a cell detects the presence of foreign DNA such as the one the researchers introduced, it shuts down production of proteins to prevent the spread of viruses.

"What we've described is that introducing these DNAs leads to a different detection system in the cell that, instead of shutting down protein expression, increases expression," said Dudley.

When the researchers combined this protein-boosting DNA with genes for other novel proteins and introduced them into host cells, those proteins were also produced at a much higher rate than with traditional methods of delivering genes. Dudley suggests that including this extra bit of genetic material could be applied to a wide range of research problems to increase the production of specific proteins within cells.

Dudley's co-authors are Yongqiang Gou, Hyewon Byun, Adam E. Zook, Gurvani B. Singh, Andrea K. Nash and Mary M. Lozano.

This research was supported by the National Institutes of Health.

Read the paper "Retroviral vectors elevate coexpressed protein levels in trans through cap-dependent translation": http://www.pnas.org/content/early/2015/03/02/1420477112.full.pdf+html

 

MORE INFO

In case you're wondering how the traditional method for delivering genes into host cells works, here's a rough outline:

To introduce DNA and associated genes into a host, scientists often start with a virus. Viruses are good at getting into host cells, and some viruses can insert their own genes into the host's DNA, essentially turning a healthy cell into a virus factory. Scientists strip out all of the viral genes except those that are needed to do this genetic insertion trick and, in their place, add genes that the scientists want added to the host's DNA. These genes usually lead the host cell to create new proteins or to increase or decrease production of ones it already makes.

As we noted in the press release, Dudley and her team didn’t set out to improve on this traditional method. They were using it to try and understand how retroviruses similar to HIV manipulate the host cell to prevent an immune response.

For a model system, Dudley and her team used human cells living in a dish and a virus related to HIV that causes cancers in mice. They suspected that the virus needed a certain host cell protein, p97/VCP, to avoid an immune response. So, they wondered, what if we added some genetic material that reduced the amount of p97/VCP produced by the host cells? Would that make the virus vulnerable to an immune response?

They inserted into human cells a bit of genetic material known as a lentivirus vector expressing a small hairpin RNA (shRNA) that, according to past research, should have caused the cells to produce less p97/VCP. Instead, they observed the opposite. These results suggested that lentiviruses and other retroviruses contain sequences that increase expression of co-introduced genes, such as those used for DNA vaccines and gene therapy.

The concept of DNA vaccines has been around for a couple of decades, but so far, none has been approved for general use in the U.S. Two different DNA vaccines designed to treat multiple sclerosis are in human clinical trials.

In the case of multiple sclerosis, an autoimmune disease, the DNA vaccines target not a virus but a certain type of immune cell produced by the human body that attacks nerve cells in the body. In other words, the goal of such a DNA vaccine is to train one part of the immune system to attack another, albeit wayward, part of the immune system. It's akin to using your left arm to hold back your right arm to prevent it from getting into a fight.

Despite some early missteps, the field of gene therapy has had some recent successes.

Children with adenosine deaminase severe combined immunodeficiency disease (ADA-SCID)— an extremely rare genetic condition also sometimes called "bubble kid" disease because those with the condition have no functioning immune system and thus have to live in sterile environments to avoid infection — developed fully functioning immune systems after a treatment using retroviruses to modify their own stem cells (Hacein-Bey-Abina et al. New England Journal of Medicine 2014). According to the National Institutes of Health, ADA-SCID is estimated to occur in approximately 1 in 200,000 to 1 million newborns worldwide.

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Thursday, 23 November 2017

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